Answer:
US desire to create a buffer zone in Eastern Europe
Explanation:
After the World War II ended, the countries that were on the wining side started to negotiate about how the continent would be divided, organized, and of course they tried to implement and force their own ideologies. This immediately created lot of tensions between the USSR and the US.
Among the numerous things on which the USSR and US failed to make an agreement, was also the US desire to create a buffer zone in Eastern Europe. Basically, the US wanted the territory from Poland's western border to the USSR's western border to be a buffer zone.
The USSR didn't fancied this. Instead, the USSR saw all territory in Eastern Europe as its zone of influence and control after the war, and on top of it it planned on making it its stronghold. What the US was suggesting was seen as conflict of interest, but also a military threat on the border, so immediately the tensions rose between the two.
